5. Let X be a discrete random variable. The following table shows its possible values r and the associated probabilities P(X-)-f(x) 013 f(x) 2/8 3/8 2/8 1/8 (a) Verify that f(x) is a probability mass function (b) Calculate P(X 2). c) Find the cumulative distribution function of X (d) Compute the mean and the variance of X